Thermal-equilibrium defects in undoped hydrogenated amorphous silicon, silicon-carbon, and silicon-nitrogen

Temperature dependence of the thermal-equilibrium defect density in undoped a-Si:H, a-Si1-xCx:H, and a-Si1-xNx:H is obtained both by in situ electron-spin-resonance (ESR) measurements at elevated temperatures and by ESR measurements of frozen-in defects at room temperature. The experimental results confirm that the defects in these alloy films, even for films with the defect density as high as 1017 cm-3, can reach thermal equilibrium above a certain temperature (200350°C). Thickness dependence of the defect density after various thermal treatments shows that only the bulk defect density increases with temperature, with the exception that thin a-Si:H films (<1 m) exhibit some extra increase. Results of ESR, light-induced ESR (LESR), and constant-photocurrent method (CPM) measurements indicate that the charged-defect density in these films does not appreciably increase with temperature. Relaxation of the frozen-in defect density follows a stretched exponential form and the relaxation time increases with the defect density in these alloys.